Methods and devices for polyaxial screw alignment

ABSTRACT

Devices and methods for aligning the components of polyaxial screws are described herein. In one embodiment, an alignment instrument includes an elongate frame having a longitudinal axis and a plurality of connection caps slidably disposed along the elongate frame. Each connection cap can removably couple to a polyaxial screw extension tube and selectively lock relative to the elongate frame such that a distance between the plurality of connection caps and an angular orientation of each connection cap relative to the elongate frame is maintained. The instrument can also include a transverse angle indicator to indicate an angular orientation of the elongate frame in a plane transverse to the longitudinal axis of the elongate frame. The device can, for example, capture the orientation of a plurality of polyaxial screws during spinal surgery such that the screws can be returned to the same orientation after manipulation to correct a spinal deformity, etc.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/961,065 filed on Dec. 7, 2015 entitled “METHODS AND DEVICES FORPOLYAXIAL SCREW ALIGNMENT,” and now issued as U.S. Pat. No. 9,999,448.U.S. patent application Ser. No. 14/961,065 is a continuation of U.S.patent application Ser. No. 13/830,548 filed on Mar. 14, 2013, entitled“METHODS AND DEVICES FOR POLYAXIAL SCREW ALIGNMENT,” and now issued asU.S. Pat. No. 9,241,742. Each of these applications is herebyincorporated by reference in its entirety.

FIELD

The present invention relates to methods and devices for use in spinalsurgery, and in particular to instruments and methods for use duringspinal fixation procedures.

BACKGROUND

Spinal fixation devices are used in orthopedic surgery to align and/orfix a desired relationship between adjacent vertebral bodies. Suchdevices typically include a spinal fixation element, such as arelatively rigid fixation rod, that is coupled to adjacent vertebrae byattaching the element to various anchoring devices, such as hooks,bolts, wires, or screws. Alternatively, two rods can be disposed on thelateral or anterior surface of the vertebral body in a substantiallyparallel relationship. The fixation rods can have a predeterminedcontour that has been designed according to the properties of the targetimplantation site and, once installed, the rods hold the vertebrae in adesired spatial relationship, either until desired healing or spinalfusion has taken place, or for some longer period of time.

Spinal fixation devices can be anchored to specific portions of thevertebra. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone. Suchscrews typically include a threaded shank that is adapted to be threadedinto a vertebra, and a receiving member having a U-shaped slot forseating the fixation rod. The receiving member can be monoaxial and thusfixed relative to the threaded shank, or it can be polyaxial and thusmovable relative to the threaded shank. Polyaxial screws can facilitatepositioning of the fixation rod therein. Extension members are oftencoupled to the receiving member, especially in minimally invasiveprocedures, to provide a pathway through tissue to the receiving member.A set-screw, plug, or similar type of closure mechanism, is used to lockthe fixation rod into the rod receiving member of the pedicle screw.

While current spinal fixation systems have proven effective,difficulties are still encountered in various spinal procedures, such aswhen correcting spinal deformities. For example, the use of polyaxialscrews in these operations can aid in capturing a rod or other spinalfixation element within the receiving member of the polyaxial screw dueto the ability of the receiving member to move relative to the threadedshank implanted in the patient's vertebra. However, the movementprovided by polyaxial screws can limit a surgeon's control when applyingcorrective forces to the screw in order to effect movement of thevertebra. Various devices exist to lock a polyaxial screw in a monoaxialconfiguration, but these devices can be problematic as well becausesurgeons often cannot tell when the receiving member is correctlyoriented with respect to the threaded shank implanted within thevertebra. In particular, locking the polyaxial screw in a monoaxialconfiguration when the receiving member is angled relative to thethreaded shank can create large moment forces on the screw during theapplication of corrective forces. To combat these forces, surgeons oftenwant to lock the polyaxial screw in a monoaxial configuration when thereceiving member is aligned with the threaded shank (i.e., thelongitudinal axes of the receiving member and the threaded shank arecoaxial). Because there is not an easy and cost-effective way to align apolyaxial screw in a coaxial configuration, surgeons often utilizevarious combinations of polyaxial, monoaxial, and uniplanar screws (thelatter provides relative motion between the receiving member andthreaded shank in only a single plane).

The use of multiple screw types, however, can be problematic becausethey add to the complexity of an already technically challengingprocedure. Furthermore, beyond the addition of the screws themselves,the use of additional screw types can require that additionalinstrumentation be present in the operating room as well. Surgeons mayneed additional training on the use of the different screw types andtheir associated instrumentation, and costs associated with sterilizingand maintaining the instrumentation and implants are also increased.Still further, monoaxial and, to a lesser degree, uniplanar screws lackthe ability to conform to a rod or other spinal fixation element, whichcan increase the difficulty of capturing and approximating a rod orother spinal fixation element during a procedure.

Accordingly, there is a need in the art for methods and devices thatallow surgeons to utilize polyaxial screws in a wider range of surgicalprocedures. In particular, there is a need for methods and devices thatallow for rod capture via polyaxial movement of a screw receiving memberwhile also allowing a surgeon to selectively lock the receiving memberin coaxial alignment with an implanted shank after rod capture.

SUMMARY

The present invention generally provides methods and devices forpolyaxial screw alignment that allow surgeons to position the componentsof one or more polyaxial screws in a coaxial orientation at any point inthe procedure. The methods and devices described herein generallyinvolve recording and/or capturing the orientation of one or morepolyaxial screws after implantation and prior to rod capture when analignment device can be coupled to both the receiving member and thethreaded shank of a polyaxial screw to ensure that the two are incoaxial alignment. The deformity correction or other spinal procedurecan then proceed as usual, and a surgeon can later return the one ormore polyaxial screws to a coaxial orientation despite the fact that thealignment shaft can no longer be used due to the presence of a spinalfixation rod or other element in the receiving member of the one or morescrews.

The orientation of the one or more screws can be captured using avariety of devices and methods. In some embodiments, for example, anelongate frame can be coupled to the one or more polyaxial screws andselectively locked to maintain their relative position and orientationin a plane extending along a longitudinal axis of the frame.Furthermore, the frame can include a transverse angle indicatorconfigured to indicate an angular orientation of the frame in a planetransverse to the longitudinal axis of the frame. By coupling theelongate frame to the one or more polyaxial screws when the alignmentshaft is present and subsequently matching the orientation of the one ormore screws to the elongate frame at a later time when the alignmentshaft is not present, a surgeon can be sure that the one or morepolyaxial screws have been returned to a coaxial orientation.

In other embodiments, an image guidance system (IGS) or some otherprecision positioning system can be used in place of a locking frame.Regardless, the procedure entails recording and/or capturing theposition and orientation of one or more polyaxial screws when analignment shaft is present in the screw to ensure its alignment, andthen guiding a surgeon to return the polyaxial screw to the coaxiallyaligned orientation at a later time when the alignment shaft is notpresent.

In one aspect, a polyaxial screw alignment instrument is provided thatincludes an elongate frame having a longitudinal axis extendingtherethrough, and a plurality of connection caps slidably disposed alongthe elongate frame. Each connection cap can be configured to removablycouple to a polyaxial screw extension tube and to selectively lockrelative to the elongate frame such that a distance between theplurality of connection caps and an angular orientation of eachconnection cap relative to the elongate frame can be maintained. Thealignment instrument can further include a transverse angle indicatorconfigured to indicate an angular orientation of the elongate frame in aplane transverse to the longitudinal axis of the elongate frame.

The methods and devices described herein can include a number ofadditional features and/or variations, all of which are consideredwithin the scope of the present invention. For example, in someembodiments the plane in which the transverse angle indicator measuresan angular orientation is perpendicular to the longitudinal axis of theelongate frame. In other embodiments, the plane in which the transverseangle indicator measures an angular orientation can be offset by someother angle from the longitudinal axis of the elongate frame.Furthermore, in some embodiments, the elongate frame can be configuredto measure the angular orientation and distance between a plurality ofpolyaxial screws in the transverse plane of the body, and the transverseangle indicator can be configured to measure the angular orientation ofthe elongate frame in the sagittal plane of the body, as described inmore detail below.

A number of different mechanical devices can be employed as thetransverse angle indicator. For example, in some embodiments, thetransverse angle indicator can include a bubble level coupled to theelongate frame. The bubble level can be, for example, rotatably coupledto the frame such that it can be rotated to a level position to mark theangular orientation of the elongate frame. In other embodiments, thetransverse angle indicator can include an angular scale coupled to theelongate frame. The angular scale can, in some embodiments, also berotatably coupled to the elongate frame such that a user can align anedge of the frame with the vertical or horizontal and read off theangular orientation of the elongate frame. Alternatively, the scale canbe rigidly coupled to the elongate frame and utilize a hanging plumbline or other method known in the art to indicate the angularorientation of the elongate frame. In still other embodiments, thetransverse angle indicator can include an arm coupled to the elongateframe and an operating surface. The arm can be adjustable and can serveto couple the frame to a fixed frame of reference, such as the operatingsurface. The angular orientation of the arm can be captured ormaintained with respect to the operating surface. In other embodiments,a surface other than the operating surface can be utilized, so long asit provides a fixed frame of reference for anchoring the adjustable arm.

In other embodiments, each of the plurality of connection caps caninclude a thumbscrew configured to selectively lock the connection caprelative to the elongate frame when tightened. For example, thethumbscrew can be loosened to allow the connection cap to slide alongthe elongate frame and rotate relative thereto, but upon tightening canrigidly fix the connection cap to the elongate frame such that it doesnot slide or rotate.

In another aspect, a polyaxial screw alignment system is provided thatincludes a plurality of polyaxial screws having a threaded shank and areceiving member coupled to the threaded shank that can move polyaxiallywith respect to the threaded shank. The system can further include aplurality of extension tubes, each extension tube configured to becoupled to the receiving member of one of the plurality of polyaxialscrews such that a longitudinal axis of the extension tube and alongitudinal axis of the receiving member are maintained in a coaxialorientation. The system can also include a plurality of alignmentshafts, each alignment shaft configured to be coupled to one of theplurality of polyaxial screws such that a longitudinal axis of thethreaded shank and a longitudinal axis of the receiving member aremaintained in a coaxial orientation. The system can further include apolyaxial screw alignment instrument having an elongate frame and aplurality of connection caps slidably disposed thereon, each connectioncap configured to be coupled to a proximal end of one of the pluralityof extension tubes and selectively locked relative to the elongate frameto maintain a distance between the plurality of connection caps and anangular orientation of each of the connection caps relative to theelongate frame, as well as a transverse angle indicator that indicatesan angular orientation of the elongate frame of the polyaxial screwalignment instrument in a plane transverse to a longitudinal axis of theelongate frame.

In some embodiments, the transverse angle indicator can include a bubblelevel coupled to the elongate frame. In other embodiments, however, thetransverse angle indicator can include an angular scale coupled to theelongate frame. In still other embodiments, the transverse angleindicator can include an arm coupled to the elongate frame and anoperating surface.

In certain embodiments, each of the plurality of alignment shafts canthreadably engage with the receiving member of one of the plurality ofpolyaxial screws. The threaded interface between the receiving memberand the alignment shaft can ensure that a longitudinal axis of thereceiving member is coaxially aligned with a longitudinal axis of thealignment shaft. Moreover, in some embodiments, each of the plurality ofalignment shafts can include a protrusion formed on a distal end thereofthat interfaces with a recess formed in the threaded shank of thepolyaxial screw. For example, the alignment shaft can be a single-piecemember and the protrusion can include a feature that is accepted withina recess formed at the proximal end of the threaded shank to allow thealignment shaft to rotate the threaded shank. The interface of theprotrusion of the alignment shaft and the recess of the threaded shankcan ensure that a longitudinal axis of the threaded shank is coaxiallyaligned with a longitudinal axis of the alignment shaft. In anotherembodiment, the alignment shaft can be a two-piece member, which assistsin coaxial alignment and also enables driving of the threaded shank. Inthe two-piece embodiment the shaft and external threads are similar tothe one-piece embodiment except that a lumen extends longitudinallythrough the shaft and the distal end, which includes the externalthreads. The two-piece embodiment further includes, as a second andseparate component, an elongate drive member that is configured to bepassed through the lumen so as to extend beyond the distal end of thethreaded shaft to engage the recess of the threaded shank. The separatedrive member can be manipulated independently of the threaded shaft,e.g., such as to rotate and drive the threaded shank.

In another aspect, a method of aligning polyaxial screws is providedthat includes coupling a plurality of extension tubes to receivingmembers of a plurality of polyaxial screws, and coupling a plurality ofalignment shafts to the plurality of polyaxial screws such that eachalignment shaft maintains a longitudinal axis of a receiving member anda longitudinal axis of a threaded shank of one of the plurality ofpolyaxial screws in a coaxial orientation. The method can furtherinclude coupling a polyaxial screw alignment instrument to proximal endsof the plurality of extension tubes and selectively locking thepolyaxial screw alignment instrument to indicate a distance between andan angular orientation of each of the plurality of extension tubesrelative to a longitudinal axis of the polyaxial screw alignmentinstrument. The method can also include indicating an angularorientation of the polyaxial screw alignment instrument in a planetransverse to the longitudinal axis of the polyaxial screw alignmentinstrument.

In certain embodiments, the method can also include removing thepolyaxial screw alignment instrument from the proximal ends of theplurality of extension tubes, and removing the plurality of alignmentshafts from the plurality of polyaxial screws. Still further, the methodcan include passing a spinal fixation element through the receivingmember of at least one of the plurality of polyaxial screws, andre-coupling the polyaxial screw alignment instrument to the proximalends of the plurality of extension tubes to return each of the pluralityof polyaxial screws to an orientation wherein a longitudinal axis of thereceiving member and a longitudinal axis of the threaded shank arecoaxial.

In some embodiments, the method can include inserting a set screw intoeach of the plurality of polyaxial screws after re-coupling thepolyaxial screw alignment instrument to maintain the coaxial orientationof the receiving member and the threaded shank. The set screw is oneexample of a closure mechanism that can be used to temporarily orpermanently secure the orientation of the polyaxial screw, as well asits position and orientation with respect to a spinal fixation elementsuch as a rod, plate, etc.

In certain embodiments, the plurality of polyaxial screws can includetwo polyaxial screws implanted bilaterally in a patient's vertebra.Surgeons often work on a single vertebral level at a time, or on asingle vertebra and its closest adjacent vertebra. Accordingly, thepolyaxial screw alignment instruments described herein can beparticularly suited to capturing the orientation of neighboringpolyaxial screws implanted bilaterally in a single vertebra of apatient. In other embodiments, however, the polyaxial screw alignmentinstruments described herein can be used in alternative locations,including, for example, in capturing the orientation of a plurality ofpolyaxial screws extending across a plurality of vertebral levels on oneside of the spine.

In another aspect, a method of aligning polyaxial screws is providedthat includes coupling an extension tube to a receiving member of apolyaxial screw where the extension tube includes features recognizableto a surgical image guidance system. The method can further includecoupling an alignment shaft to the polyaxial screw such that thealignment shaft can maintain a longitudinal axis of the receiving memberand a longitudinal axis of a threaded shank of the polyaxial screw in acoaxial orientation, as well as measuring the three-dimensional positionand angular orientation of the extension tube using the surgical imageguidance system.

In some embodiments, the method can also include removing the alignmentshaft from the polyaxial screw after measuring the three-dimensionalposition and angular orientation of the extension tube, and passing aspinal fixation element through the receiving member of the polyaxialscrew. The method can further include measuring the three-dimensionalposition and angular orientation of the extension tube using thesurgical image guidance system a second time, as well as adjusting theextension tube to place the longitudinal axis of the receiving memberand the longitudinal axis of the threaded shank in a coaxial orientationbased on guidance from the surgical image guidance system.

In other embodiments, the method can further include inserting a setscrew into the polyaxial screw after adjusting the extension tube tomaintain the coaxial orientation of the receiving member and thethreaded shank. As described above, in some embodiments, the polyaxialscrew can be implanted in a patient's vertebra.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects and embodiments of the invention described above will bemore fully understood from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a front view of a prior art polyaxial bone screw;

FIG. 2 is a cross-sectional view of another version of a prior artpolyaxial screw;

FIG. 3 is a perspective view of an alternative embodiment of a prior artreceiving member of a polyaxial screw;

FIG. 4 is a perspective view of a prior art polyaxial screw extensiontube coupled to the polyaxial screw of FIG. 1;

FIG. 5 is a front view of the prior art polyaxial screw extension tubeof FIG. 4;

FIG. 6 is an illustration of the various anatomical planes anddirections of the body;

FIG. 7 is a perspective view of one embodiment of a polyaxial screwalignment instrument;

FIG. 8 is a top view of the polyaxial screw alignment instrument of FIG.7;

FIG. 9 is a rear view of the polyaxial screw alignment instrument ofFIG. 7;

FIG. 10 is an exploded view of the polyaxial screw alignment instrumentof FIG. 7;

FIG. 11 is a cross-sectional view of a portion of the polyaxial screwalignment instrument of FIG. 7;

FIG. 12A illustrates the operation of one embodiment of a connectioncap;

FIG. 12B illustrates another view of the operation of the connection capof FIG. 12A;

FIG. 13A illustrates one embodiment of a selective locking mechanism ofa polyaxial screw alignment instrument;

FIG. 13B illustrates an alternative embodiment of a selective lockingmechanism of a polyaxial screw alignment instrument;

FIG. 13C illustrates an alternative embodiment of a selective lockingmechanism of a polyaxial screw alignment instrument;

FIG. 14 is a perspective view of an alternative embodiment of apolyaxial screw alignment instrument;

FIG. 15 is a perspective view of an alternative embodiment of apolyaxial screw alignment instrument;

FIG. 16 illustrates a plurality of polyaxial screws having extensiontubes coupled thereto implanted in a patient's vertebra;

FIG. 17 illustrates the polyaxial screws and extension tubes of FIG. 16having alignment shafts coupled thereto;

FIG. 18 is a perspective view of one embodiment of an alignment shaft;

FIG. 18A is a perspective view of one embodiment of an alignment shaftassembly;

FIG. 19 illustrates the polyaxial screws, extension tubes, and alignmentshafts of FIG. 17 having a polyaxial screw alignment instrument coupledthereto;

FIG. 20 is a perspective view of one embodiment of a polyaxial screwextension tube including features recognizable by an image guidancesystem (IGS); and

FIG. 21 is an alternative embodiment of a polyaxial screw alignmentinstrument.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the devices and methodsdisclosed herein. One or more examples of these embodiments areillustrated in the accompanying drawings. Those skilled in the art willunderstand that the devices and methods specifically described hereinand illustrated in the accompanying drawings are non-limiting exemplaryembodiments and that the scope of the present invention is definedsolely by the claims. The features illustrated or described inconnection with one exemplary embodiment may be combined with thefeatures of other embodiments. Such modifications and variations areintended to be included within the scope of the present invention.

The present invention is generally directed to devices and methods forpolyaxial screw alignment. More particularly, the methods and devicesdescribed herein can allow a surgeon to reliably position one or morepolyaxial screws in an orientation that coaxially aligns a longitudinalaxis of a receiving member and a longitudinal axis of a threaded shankof each screw. This can be advantageous because surgeons often desirepolyaxial movement of a receiving member relative to a threaded shankduring certain stages of spinal surgery (e.g., rod capture), but wantmonoaxial rigidity and control during other stages (e.g., deformitycorrection, distraction, compression, etc.). Furthermore, locking apolyaxial screw in an orientation in which the longitudinal axes of thereceiving member and the threaded shank are angularly offset can subjectthe screw to large or misdirected moment forces when corrective forcesare applied. Using prior art devices and methods, however, there is nota reliable and effective way to determine when the components of apolyaxial screw are in coaxial alignment, especially after a rod orother spinal fixation element has been seated within the receivingmember of the screw. The devices and methods described herein addressthis shortcoming by capturing the orientation of one or more polyaxialscrews when their coaxial alignment can be ensured (e.g., prior to rodcapture) and allowing a user to easily return the screw to that sameorientation at a later point in the procedure (e.g., after rod capture).

FIG. 1 illustrates one embodiment of a polyaxial screw 100 known in theart. The polyaxial screw 100 includes a bone anchor 102, such as apedicle screw, having a proximal head 104 and a distal bone-engagingportion 106, which in the illustrated exemplary embodiment is anexternally threaded screw shank. The polyaxial screw 100 also includes areceiving member 108 that is configured to receive and couple a spinalfixation element, such as a spinal rod or spinal plate, to the polyaxialscrew 100.

The receiving member 108 may be coupled to the bone anchor 102 in anymanner known in the art. For example, the bone anchor 102 may beadjustable to multiple angles relative to the receiving member 108. Thisis in contrast to monoaxial bone screws, in which the bone anchor 102and the receiving member 108 are not movable relative to one another. Anexemplary polyaxial bone screw is described U.S. Pat. No. 5,672,176,which is herein incorporated by reference in its entirety.

The receiving member 108 of the illustrated exemplary embodimentincludes a proximal end 110, a distal end 112, and a recess or slot 114for receiving a spinal fixation element, such as a spinal rod. Theproximal end 110 of the receiving member 108 has a first bore 116 formedtherein that defines a first bore axis 118 and communicates with therecess 114 such that a spinal fixation element may be positioned throughthe first bore into the recess 114. The first bore axis 118 can beconsidered the longitudinal axis of the receiving member 108. The distalend 112 has a second bore 120 opposite the first bore 116 that defines asecond bore axis 122 and is designed to receive the head 104 of the boneanchor 102 to couple the bone anchor to the receiving member 108. In theillustrated exemplary embodiment, the head 104 is seated within thesecond bore 120. As the exemplary illustrated embodiment of the boneanchor assembly is polyaxial, the bone anchor 102 is free to rotaterelative to the receiving member 108 such that the longitudinal axis 124of the bone anchor 102 is positionable at an angle relative to thesecond bore axis 122 of the receiving member 108 (in FIG. 1, the firstbore axis 118, second bore axis 122, and longitudinal axis 124 of thebone anchor 102 are coaxial). The second bore 120 may be spherically orconically shaped to facilitate adjustment of the bone anchor 102relative to the receiving member 108. In the exemplary embodiment, thereceiving member 108 has a generally U-shaped cross-section defined bytwo legs 124A and 124B separated by recess 114. Each leg 124A, 124B isfree at the proximal end 110 of the receiving member 108.

The receiving member 108 may be configured to receive a closuremechanism that locks a spinal fixation element within the recess 114.The closure mechanism may be a cap that is advanceable through the firstbore 116 of the receiving member 108 and seats against the spinalfixation element. For example, the cap may have external threads thatengage internal threads provided in the receiving member 108, e.g., onthe legs 124A, 124B. Any type of conventional closure mechanism may beemployed, including, for example, non-threaded caps, multi-componentclosure mechanisms, and/or external caps.

The receiving member 108 of the exemplary polyaxial screw 100 caninclude features allowing it to be releasably connected to a variety ofinstruments, such as the polyaxial screw extension tube described below.For example, the receiving member 108 may include at least one groovethat is configured to receive a portion of an instrument to releasablyconnect the instrument to the polyaxial screw. The size, shape,position, and number of grooves can be varied depending on, for example,the instrument employed and the type of connection desired. In certainembodiments, for example, at least one arcuate groove may be provided onan exterior surface of the proximal end 110 of the receiving member 108.In other exemplary embodiments, at least one arcuate groove may beprovided on an interior surface of the proximal end 110 of the receivingmember 108. In the illustrated exemplary embodiment, each leg 124A and124B may be provided with an arcuate groove 130A, 130B, respectively, atthe free, proximal end of the leg 124A, 124B. The grooves 130A, 130B mayextend about a portion or the entirety of the circumference of theproximal end of each leg 124A, 124B. Each groove 130A, 130B may have asize and shape that is complementary in size and shape to a projectionor other feature provided on the instrument, as described in more detailbelow.

FIG. 2 illustrates the polyaxial screw 100 in cross-section. Inparticular, the spherical head 104 of the bone anchor 102 is shownextending through the second bore 120 formed in the distal end of thereceiving member 108 and seated within a spherical seat in the receivingmember. The head 104 can include a recess 202 or other feature that canreceive a driver or other instrument, such as the alignment shaftdescribed below. Also shown is a compression member 204 that resideswithin the recess 114 of the receiving member 108. The compressionmember 204 can include an inner lumen that allows a driver or otherinstrument to access the recess 202 of the bone anchor 102. Furthermore,the compression member 204 can include features formed at its proximaland distal ends that are configured to interface with a spinal fixationelement, such as the spinal fixation rod 206, and the head 104 of thebone anchor 102, respectively. For example, the compression member 204can include a hemispherical recess 208 formed at its distal end that canmirror the shape of the head 104 of the bone anchor 102. At its proximalend, the compression member 204 can include a U-shaped recess 210 thatis configured to seat a spinal fixation element, such as the spinalfixation rod 206.

The compression member 204 can be configured to travel within the recess114 of the receiving member 108 along the first bore axis 118 between afirst position in which the compression member allows polyaxial movementof the head 104 within the receiving member 108 and a second position(shown by arrows 212 in FIG. 2) in which the compression member locksthe orientation of the bone anchor 102 with respect to the receivingmember 108. This is typically accomplished with the use of a closuremechanism, such as the outer set screw 214. As the outer set screw 214is threaded into the proximal end of the receiving member 108, it canexert a downward force on the compression member 204 (shown by arrows216 in FIG. 2), thereby pushing the compression member 204 from thefirst position to the second position and locking the orientation of thebone anchor 102 and the receiving member. The outer set screw 214 canitself include an inner lumen to receive an inner set screw 218 that canbe used to lock the receiving member in a particular orientation andposition along the spinal fixation rod 206 by pressing the rod into theU-shaped recess 210 of the compression member (shown by arrows 216 inFIG. 2).

There are a number of variations on the polyaxial screw 100 known in theart. For example, FIG. 3 illustrates an embodiment of a polyaxial screwreceiving member 300 that is biased to a particular angle or range ofangles to provide a favored angle to the bone anchor 102. This favoredangle can aid in rod capture during a spinal procedure as the receivingmember 108 can have additional range of motion in one direction, e.g.,laterally away from the spinal column. In favored angle embodiments, thesecond bore axis 122 can be positioned at an angle α (other than 0°) tothe first bore axis 118. Exemplary favored angle bone screws aredescribed in U.S. Pat. Nos. 6,736,820 and 6,974,460, both of which areherein incorporated by reference in their entirety.

The receiving member 108 can be configured to couple with a variety ofinstruments, as described above. FIGS. 4-5 illustrate one embodiment ofsuch an instrument known as a polyaxial screw extension tube. Theextension tube 400 is in the form of a generally elongate, cylindricaltube having an inner lumen 402 formed therein and defining alongitudinal axis 404 that extends between proximal and distal ends406A, 406B. The size of the extension tube 400 can vary depending onintended use, but it should have a length l that allows the proximal end406A of the extension tube 400 to be positioned outside a patient's bodywhile the distal end 406B of is coupled to the receiving member 108 ofthe polyaxial screw 100 that is implanted in a patient's spine. As aresult, the extension tube 400 can provide a more readily accessiblecomponent that can be manipulated by a surgeon or other tool to impartcorrectional forces to the polyaxial screw 100 and the vertebra in whichit is implanted. Further, the inner diameter d_(i) of the extension tube400 be sufficiently large to accommodate a diameter or width of a spinalfixation element, closure mechanism, or other tool (e.g., the alignmentshaft described below) to be introduced therethrough to access thepolyaxial screw.

The extension tube 400 can, in some embodiments, optionally include atleast one sidewall opening or slot 408 formed therein and extendingproximally from the distal end 406B thereof. A person of skill in theart will understand that such sidewall openings or slots are notnecessary in some embodiments. The openings 408 can allow a spinalfixation element to be positioned lengthwise between two adjacentpolyaxial screws 100 and attached extension tubes 400 such that thespinal fixation element extends in an orientation that is substantiallytransverse to the longitudinal axis 404 of the extension tube 400, i.e.,that crosses the longitudinal axis 404 of the extension tube 400. Theexact position of the spinal fixation element with respect to thelongitudinal axis 404 will of course vary depending on the configurationof the spinal fixation element. The shape and size of the openings 408can also vary depending on the configuration of the spinal fixationelement, but the openings 408 can have a generally elongate shape with awidth w that is sufficient to accommodate the diameter of the spinalfixation element. The openings 408 can extend over any length of theextension tube 400. In some embodiments, the openings 408 can extendsuch that a proximal portion of each opening 408 is positioned outside apatient's body while the extension tube 400 is in use, thus allowing aspinal fixation element to be externally positioned through the openings408 and then moved distally to be implanted.

Continuing to refer to FIGS. 4-5, in use, the extension tube 400 can beadapted to attach to the receiving member 108 of the polyaxial screw100. Accordingly, the distal end 406B of the extension tube 400 caninclude one or more mating elements 410 formed thereon or therein forengaging the receiving member 108. Suitable mating elements include, forexample, threads, a twist-lock engagement, a snap-on engagement, or anyother technique known in the art, and in an exemplary embodiment themating elements can be formed on opposed inner surfaces of the distalend 406B of the extension tube 400. In some embodiments, the matingelements 410 can be configured to couple the extension tube 400 to thereceiving member 108 such that the longitudinal axis 404 of theextension tube 400 is coaxial with the longitudinal axis 118 of thereceiving member 108. A sleeve (not shown) or other device, preferablyhaving sidewall openings that correspond with the sidewall openings 408formed in the extension tube 400, can also be placed over the extensiontube 400, and optionally over the receiving member 108 as well, toprevent disengagement of the extension tube 400 from the receivingmember 108 during use. Exemplary techniques for mating instruments suchas the extension tube 400 to a polyaxial screw are disclosed in U.S.Pat. No. 7,666,188, the contents of which are incorporated by referencein their entirety. A person skilled in the art will appreciate that avariety of other techniques can be used to removably mate the extensiontube 400 to a polyaxial screw.

As described above, polyaxial screws like those illustrated in FIGS. 1-3can provide a number of advantages to surgeons, but are not withoutdrawbacks. For example, the polyaxial movement of the receiving member108 relative to the bone anchor 102 can aid in capturing a rod or otherspinal fixation element after implantation in a patient's vertebra. Thissame movement, however, can limit a surgeon's control when applyingcorrective forces to the vertebra via the polyaxial screw in otherportions of the procedure. The two-part set screws described above thatcan independently lock the polyaxial movement of the screw 100 and theposition of the rod 206 can allow a surgeon to lock the screw in amonoaxial configuration, but surgeons often cannot tell if the screw isin a desired orientation when doing so. For example, surgeons often wishto lock the screw 100 in a monoaxial configuration when its receivingmember 108 and bone anchor 102 are in a coaxial orientation (i.e., thelongitudinal axis 124 of the bone anchor 102 is coaxial with thelongitudinal axis 118 of the receiving member 108) to reduce the momentforces experienced by the screw when corrective forces are applied tothe vertebra through the screw. It can be difficult to determine thisorientation due to the fact that the bone anchor 102 is implanted in thevertebra and a rod or other spinal fixation element is seated within thereceiving member 108. This problem can be exacerbated by the use offavored angle screws, as the receiving members of these screws have anon-symmetric range of motion and can move to a near-horizontalorientation in the favored direction. Surgeons can attempt to position apolyaxial screw in a coaxial orientation using a series of X-ray imagesto visualize the bone anchor 102 within the vertebra, but this is oftentime consuming, expensive, and it can expose the patient to additionalradiation.

Instead, surgeons often compromise by utilizing different types ofscrews in different portions of a spinal fixation construct. Forexample, in spinal deformity correction procedures, a primary goal canbe to align a patient's shoulders and pelvis (i.e., the top and bottomportions of the construct). Because there is a need to preciselydetermine the orientation of vertebrae in these locations, monoaxialscrews are often used at the top and bottom of a pedicle screwconstruct. The monoaxial screws allow the surgeon to locate the screw inthe vertebral body and use the exposed receiving member to indicatevertebral body orientation with a high level of precision. Monoaxialscrews, however, do not conform to a rod and therefore makeapproximating and capturing the rod or other fixation element in thepedicle screw construct more difficult. In addition, using multipletypes of screws in a procedure adds to the complexity and cost of theprocedure.

The methods and devices described herein can address these shortcomingsby allowing surgeons to efficiently and effectively align the componentsof one or more polyaxial screws in a coaxial orientation. This, in turn,can permit surgeons to utilize a single polyaxial screw type throughouta spinal fixation construct. In general, the methods described hereininclude capturing the position and angular orientation of one or morepolyaxial bone screws in a first plane, and then determining the angularorientation of the screws in a second plane transverse to the firstplane. With reference to FIG. 6, for example, a method of aligning aplurality of polyaxial screws can include capturing the distance betweenand angular orientation of the plurality of polyaxial screws in thetransverse plane of the body (i.e., in the medial/lateral directions).The plurality of polyaxial screws can be, for example, two polyaxialscrews implanted bilaterally in a vertebra of a patient. The method canfurther include capturing the angular orientation of the screws in thesagittal plane of the body as well (i.e., in the cranial/caudaldirections). Capturing the position and orientation of the screws inthese two planes can allow a surgeon to return the screws to the sameorientation at a later time and be assured that the receiving membersand threaded shanks of the screws are again coaxially aligned.

FIGS. 7-11 illustrate one embodiment of a polyaxial screw alignmentinstrument 700 that can be used to capture the position and orientationof a plurality of polyaxial screws. The instrument 700 can include anelongate frame 702 having proximal and distal ends 703A, 703B, and alongitudinal axis 704 extending therethrough. The elongate frame canhave a variety of shapes and sizes but, in some embodiments, can have arectangular shape in which a length is larger than a width or depth ofthe frame. In certain embodiments, the length of the frame can be about275 mm, with a width of about 15 mm and a depth of about 7 mm. Theelongate frame 702 can in some embodiments include recessed areas formedon either side of the frame along a length thereof, thereby giving theframe a cross-sectional shape similar to an I-beam. Furthermore, theframe can include one or more through-channels 706 extending along aportion of the elongate frame to receive a plurality of connection caps708 slidably disposed on the frame. Further, the elongate frame caninclude distance markings 710 that can be used to measure the distancebetween the plurality of connection caps 708, or between each of theplurality of connection caps 708 and a fixed point of reference on theelongate frame (e.g., the proximal end 703A of the elongate frame 702).The distance markings 710 can be imprinted on the elongate frame usingany suitable manner known in the art, including, for example, inkprinting, laser engraving, etching, grinding, etc.

As mentioned above, each of the plurality of connection caps 708 can beslidably disposed along the elongate frame 702 such that they can betranslated along at least a portion of the frame between the proximaland distal ends 703A, 703B, as shown by arrows 712. As is best shown inthe exploded view of FIG. 10, each connection cap 708 can includeseveral components that allow the connection cap to translate along thelength of the elongate frame 702, rotate relative to the frame about anaxis 1002 extending through the frame, and selectively lock relative tothe frame such that neither rotation nor translation is permitted.

In the illustrated embodiment, and with particular reference to FIG. 10,each connection cap 708 can include a connection cap body 1004 having aninner lumen 1006 configured to receive the proximal end of a polyaxialscrew extension tube (e.g., polyaxial screw extension tube 400 discussedabove), and a cantilever shaft 1008 extending from a sidewall thereofthat is configured to extend through the channel 706 formed in theelongate frame 702. The connection cap body can have a variety of shapesand sizes but, in some embodiments, can be sized such that the innerlumen 1006 extending therethrough is large enough to receive the outerdiameter of an extension tube.

Slidably disposed within the connection cap body 1004 can be anextension tube locking member 1010 that is configured to selectivelylock the connection cap body to the proximal end of a polyaxial screwextension tube. The tube locking member 1010 can also include an innerlumen formed therein, and the inner lumen can be divided into anenlarged portion 1012 and a constricted portion 1014. The enlargedportion 1012 can have a diameter at least as large as the diameter ofthe inner lumen 1006 of the connection cap body 1004 so that theproximal end of a polyaxial screw extension tube can be receivedtherethrough. The constricted portion 1014, however, can have a reduceddiameter configured to interface with a notch or other complementaryfeature formed on an outer surface of a polyaxial screw extension tube.FIG. 11 illustrates the connection cap 708 in cross section and showsthe interaction between the connection cap body 1004 and the tubelocking member 1010. In particular, the tube locking member 1010 can beslidably disposed within the connection cap body 1004 and its movementcan be constrained by an alignment pin 1015. In this configuration, thetube locking member 1010 can move between a first position in which theenlarged portion 1012 of the inner lumen of the tube locking member 1010is aligned with the inner lumen 1006 of the connection cap body 1004,and a second position in which the constricted portion 1014 of the innerlumen of the tube locking member 1010 is aligned with the inner lumen1006 of the connection cab body 1004 (as shown in FIG. 11).

FIGS. 12A-12B illustrate the resulting operating of the connection cap708. To begin, the tube locking member 1010 can be moved to the firstposition such that the full diameter of the inner lumen 1006 of theconnection cap body 1004 is open. As shown in FIG. 12A, the connectioncap 708 can then be lowered on top of a proximal end of a polyaxialscrew extension tube 1200. The extension tube 1200 can include anannular groove 1202 formed at a proximal end thereof that has an outerdiameter substantially equal to the diameter of the constricted portion1014 of the tube locking member 1010. To releasably lock the connectioncap 708 to the extension tube 1200, a user can slide the tube lockingmember 1010 from the first position (as shown in FIG. 12A) to the secondposition (as shown in FIG. 12B), which can bring the constricted portion1014 of the tube locking member 1010 into contact with the annulargroove 1202 formed in the extension tube 1200.

Referring back to FIG. 10, a retaining washer 1016 can be placed overthe shaft 1008 such that it abuts against the connection cap body 1004and holds the alignment pin 1015 within a through-hole formed in theconnection cap body. A coil spring 1018 can be placed over the shaft1008 as well to prevent the various components of the connection cap 708from becoming loose when the connection cap 708 is not locked to theelongate frame 702.

The connection cap 708 can be coupled to the elongate frame 702 usingfirst and second sliding members 1020, 1022 disposed on opposite sidesof the elongate frame 702. The first sliding member 1020 can have ashape that complements the profile of an outer surface of the elongateframe 702. For example, and as shown in FIGS. 10-11, the first slidingmember 1020 can have a rectangular shape and include parallel recessedchannels extending along a length thereof such that the first slidingmember 1020 can fit over one three sides of the elongate frame 702. Thesecond sliding member 1022 can have a rectangular shape and can be sizedsuch that it fits within the recessed area formed on one side of theelongate frame 702. Both the first and second sliding members 1020, 1022can include through-holes formed therein that are configured to receivethe shaft 1008 of the connection cap body 1004.

Selective locking of the connection cap 708 with respect to the elongateframe 702 can be accomplished using the thumbscrew 1024 that engageswith threads formed on a portion of the shaft 1008 of the connection capbody 1004. By tightening the thumbscrew 1024, the first and secondsliding members 1020, 1022 can be compressed against the elongate frame702 such that sliding motion with respect to the elongate frame isprohibited. Furthermore, by tightening the thumbscrew 1024, theconnection cap body 1004 can be securely pressed against the firstsliding member 1020, thereby preventing the connection cap body fromrotating with respect to axis 1002. In addition, a retaining washer 1026can be rigidly coupled to the distal end of the shaft 1008 such that thethumbscrew 1024 cannot be loosened to a point where it disengages fromthe shaft 1008. Accordingly, the thumbscrew can effect the selectivelocking of the connection cap 708 with respect to the elongate framesuch that the position and angular orientation of the connection cap 708(and any polyaxial screw extension tube coupled thereto) relative to theelongate frame can be captured and/or maintained.

While FIGS. 10-13C illustrate the use of a connection cap 708 to engagea proximal portion of extension tube 1200 and thereby connect theextension tube to the elongate frame, a person of skill in the art willappreciate that alternative connection schemes can be used. For example,a variety of clamp-like elements can be used to engage either a proximalportion of the extension tube or a portion of the extension tubeintermediate the proximal and distal ends of the extension tube. Anexample of such a clamp-like element is described below and illustratedin FIG. 21.

One of skill in the art will appreciate that the embodiments describedabove provide examples of a few of many of possible mechanisms forslidably disposing a connection cap to an elongate frame such that theconnection cap can be selectively locked in position and orientationrelative to the frame. The above-described embodiments, or any otherembodiments known in the art, can be constructed in a variety of sizesdepending on intended use, size and number of polyaxial screw extensiontubes, patient anatomy, etc. Further, the components can be constructedfrom any suitable biocompatible material, such as stainless steel, or apolymer, and can be constructed using any conventional method ofmanufacturing medical devices.

For example, FIGS. 13A-13C illustrate variations on the thumbscrew 1024that can be included in the assembly of a connection cap 708. FIG. 13Aillustrates a thumbscrew 1300 having short arms to reduce the overallsize of the thumbscrew 1024. To aid in leveraging the thumbscrew 1024when selectively locking a connection cap's position and/or orientation,the thumbscrew can include one or more recesses (not shown) that canreceive a driving tool 1302. FIG. 13B illustrates an alternativeembodiment of a thumbscrew 1304 that is similar in shape to thumbscrew1024. The thumbscrew 1304 can have longer arms than the thumbscrew 1300to provide greater leverage. In such an embodiment, a tool 1306 can beconfigured to simply slide over one of the arms to extend its length andincrease a user's mechanical advantage when tightening the thumbscrew.FIG. 13C illustrates still another alternative embodiment in which acylindrical thumbscrew 1308 is provided in place of a thumbscrew havingseparate arms. One of skill in the art will appreciate that there are avariety of other possible configurations for the thumbscrew or othercomponents of the connection cap 708 that can be used without departingfrom the teachings of the present invention. For example, although notillustrated, the thumbscrew can be oriented so as to be in a plane thatis substantially transverse or otherwise angularly oriented with respectto a longitudinal axis of the extension tube.

Referring back to FIGS. 7-10, the polyaxial screw alignment instrument700 can also include a transverse angle indicator 714 that can becoupled to the elongate frame 702. The transverse angle indicator 714can indicate an angular orientation of the elongate frame 702 in a planethat is transverse to the longitudinal axis 704 of the elongate frame.In the illustrated embodiment, the transverse angle indicator 714 caninclude a bubble level 716 rotatably coupled to the elongate frame 702at the proximal end 703A thereof. The bubble level can be configured torotate (as shown by arrows 718) in a plane that is transverse to thelongitudinal axis 704 of the elongate frame 702. In some embodiments,the plane can be perpendicular to the longitudinal axis 704. In theillustrated embodiment, for example, the plane of rotation extends alongthe longitudinal axis 720 of the bubble level 716 that is perpendicularto the longitudinal axis 704 of the elongate frame 702. As mentionedabove, however, in other embodiments the transverse plane need not beperpendicular, but can be angularly offset from the longitudinal axis704 by some other amount.

The bubble level 716 illustrated in FIGS. 7-10 can have a variety ofshapes and sizes. In the illustrated embodiment, the bubble level 716has a generally cylindrical shape that defines the longitudinal axis720. The bubble level 716 can be a sealed transparent member partiallyfilled with a liquid such that an air bubble 722 remains within thesealed member. The bubble level 716 can include any number of markings724 that can aid a user in determining when the bubble level 716 is in alevel orientation. In other embodiments, alternative bubble leveldesigns can be employed, including, for example, hemispherical bubblelevels (as shown in FIG. 19) and other known designs.

The bubble level 716 can be coupled to the elongate frame 702 by arotating member 726 such that the bubble level can be rotated within aplane transverse to the longitudinal axis 704 of the elongate frame. Therotating member 726 can have a variety of lengths, shapes, andmechanical configurations. For example, in some embodiments the rotatingmember 726 can include a cantilever shaft extending from the elongateframe 702 and a cylindrical sleeve extending from an outer surface ofthe bubble level 716. The cylindrical sleeve can include a bore formedtherein sized to receive the shaft extending from the elongate frame702, and the outer surface of the shaft and inner surface of the sleevebore can include threads to rotatably engage one another. Furthermore,in some embodiments, the rotating member 726 can include a set screw orother position-retention mechanism to allow the bubble level 716 to belocked in a particular orientation relative to the elongate frame 702.

To use the transverse angle indicator 714, a user can place the elongateframe and plurality of connection caps in a desired orientation (e.g.,by coupling the plurality of connection caps to a plurality of polyaxialscrew extension tubes, as described below) and then rotate the bubblelevel 716 until the air bubble 722 indicates that the bubble level is ina level orientation (e.g., the air bubble 722 is positioned at thecenter of the bubble level 716 between two markings 724). The user canthen lock the bubble level 716 in this orientation (if a locking featureis present) for future reference. To return the frame to the sameorientation with respect to the transverse plane, a user can simplyrotate the elongate frame 702 in the transverse plane until the bubblelevel 716 again indicates that it is in a level orientation.

FIG. 14 illustrates an alternative embodiment of a polyaxial screwalignment instrument 1400 that includes a different transverse angleindicator 1402. The transverse angle indicator 1402 includes an angularscale 1404 that can be rotatably mounted to the elongate frame 1406 at apivot point 1408. To use the transverse angle indicator 1402, a user canposition instrument 1400 in a desired orientation and then rotate theangular scale 1404 until one of its edges aligns with a vertical orhorizontal direction. The user can then correlate a marking formed onthe elongate frame 1406, or an edge of the frame itself, with a degreemarking on the angular scale 1404 to determine the angular orientationof the instrument 1406 in a plane transverse to a longitudinal axis 1410of the elongate frame 1406.

Of course, the illustrated embodiment is just one example of an angularscale that can be utilized in the polyaxial screw alignment instrument1400. For example, in other embodiments an angular scale similar to thescale 1404 can be rigidly mounted to the elongate frame 1406 and caninclude a small weight hanging from a string that can act as a verticalplumb. As the elongate frame is positioned, the hanging string can moveacross the angular scale and indicate the angular orientation of theinstrument in a plane transverse to a longitudinal axis of the elongateframe. In another embodiment, a laser or similar light emitting elementcan be rotatably mounted to the frame and configured in such a way(e.g., by the use of one of more weighted elements) that the lightemitted by the laser is always directed vertically by the effects ofgravity. As in the embodiment described above, the light can be directedto an angular scale to indicate the angular orientation of theinstrument in a plane transverse to a longitudinal axis of the elongateframe. Still further, the features of the various embodiments describedherein can be combined with one another. For example, the angular scale1402 can include a bubble level similar to the level 716 rigidly mountedthereto such that a user can more easily align the scale with a verticalor horizontal direction. In other embodiments, an angular scale can beadded to the transverse angle indicator 714 such that a user can capturethe angular orientation of the instrument 700 by recording the exactangular orientation rather than locking the bubble level 716 in anparticular orientation.

FIG. 15 illustrates still another embodiment of a polyaxial screwalignment instrument 1500 that includes another embodiment of atransverse angle indicator 1502. In the illustrated embodiment, thetransverse angle indicator 1502 can include a rigid arm 1504 rigidlycoupled at one end to the elongate frame 1506 at point 1508, androtatably coupled at the other end to an operating surface 1510 or otherfixed object at pivot point 1512. The arm 1504 can be constrained torotate about the pivot point 1512 through a single plane, e.g., theplane defined by the sidewall 1514 of the operating surface 1510. As aresult, the position of the arm can indicate the angular orientation ofthe elongate frame 1506 with respect to the operating surface 1510.Because the position and orientation of the operating surface 1510 doesnot change throughout the procedure, it can serve as a reference framefor orienting the elongate frame 1506, just as the constant direction ofgravity does in the previously-described embodiments.

The arm 1504 can include a number of previously-described features toaid a user in capturing and returning to a particular angularorientation at different times during a procedure. For example, the armcan include an angular scale coupled thereto (or disposed on thesidewall 1514 of the operating surface 1510) to allow a user to read offthe exact angular orientation of the arm 1504, or the arm can include aset screw or other retaining feature to allow the arm to be locked in agiven orientation as desired. Furthermore, the elongate frame 1506 canbe removably coupled to the arm 1504 at point 1508, and the arm can beremovably coupled to the operating surface 1510 at point 1512. This canallow the elongate frame 1506, or the elongate frame and arm 1504, to beremoved when not in use and reattached when necessary. Still further,the arm 1504 can have a telescoping length to accommodate variousoperating heights, and can be configured to attach to the operatingsurface 1510 at various locations, e.g., various locations along thelength of the operating surface sidewall 1514.

FIGS. 16-19 illustrate an exemplary method for use of a polyaxial screwalignment instrument as described herein. The method can includeimplanting in a vertebra one or more polyaxial bone screws having areceiving member that is polyaxially movable relative to a threadedshank implanted within the vertebra. In FIG. 16, for example, twopolyaxial screws 1602A, 1602B are shown implanted in a bilateralconfiguration in vertebra 1600. Each polyaxial screw 1602A, 1602B caninclude a threaded shank 1604A, 1604B and a receiving member 1606A,1606B coupled to the threaded shank 1604A, 1604B. The method can alsoinclude coupling a polyaxial screw extension tube, such as the extensiontubes 1608A, 1608B, to each of the receiving members 1606A, 1606B.

In the configuration shown in FIG. 16, the extension tubes 1608A, 1608Bare coupled to the receiving members 1606A, 1606B such that alongitudinal axis 1610A, 1610B of each extension tube is coaxial with alongitudinal axis of the receiving member it is coupled to. Furthermore,each extension tube and receiving member pair can move polyaxially withrespect to the threaded shank 1604A, 1604B that it is coupled to.

Prior to capturing a rod or other spinal fixation element within thereceiving members 1606A, 1606B of the polyaxial screws 1602A, 1602B, analignment shaft, such as the alignment shafts 1702A, 1702B, can beinserted into each of the extension tubes 1608A, 1608B. Each of thealignment shafts 1702A, 1702B can be a rigid, elongate shaft having ahandle, such as the handles 1704A, 1704B, at a proximal end thereof andan engagement portion at a distal end thereof that can be configured tointerface with both the receiving member and the threaded shank of apolyaxial screw in a manner that locks the two components in a coaxialorientation. Each alignment shaft can have a longitudinal axis 1706A,1706B extending between the proximal and distal ends thereof.

FIG. 18 illustrates one embodiment of a distal end of an alignment shaft1702 that includes an engagement portion 1802. The engagement portion1802 can include separate components configured to interface with eachof the receiving member and the threaded shank of a polyaxial screw. Inthe illustrated embodiment, for example, the engagement portion 1802 caninclude external threads 1804 configured to engage with the internalthreads formed on the receiving member, e.g., the threads formed on thelegs 124A, 124B of the receiving member 108 shown in FIGS. 1-2. Theengagement portion 1802 can also include a protrusion 1806 formed on adistal end of the alignment shaft 1702 and configured to interface witha recess or driving feature provided on the threaded shank of apolyaxial screw, e.g., the recess 202 formed in the head 104 of the boneanchor 102 shown in FIG. 2. In this embodiment engagement between thealignment shaft 1702 and the threaded shank of a polyaxial screw, suchas through protrusion 1806 and the recess of the threaded shank of apolyaxial screw) can be effective to coaxially align the threaded shankand the alignment shaft.

In another embodiment, shown in FIG. 18A, an alternative alignment shaftassembly 1703 is shown. Rather than a one-piece member such as alignmentshaft 1702 of FIG. 18, alignment shaft assembly 1703 is a two-piecemember, which is effective to coaxially align the threaded shank and thealignment shaft as well as to facilitate driving of the threaded shank.Alignment shaft assembly 1703 includes a shaft 1702′ and externalthreads 1804′ similar to the shaft 1702 and protrusion with externalthreads 1804 described above for the one-piece embodiment of FIG. 18.However, shaft 1702′ includes a lumen (not shown) extendinglongitudinally therethrough and it terminates with the external threads1804′. The two-piece embodiment further includes, as a second component,an elongate drive member that extends from a proximal handle 1811 to thedrive member 1806′, shown in FIG. 18A as protruding from the distal endof the alignment shaft 1702′. FIG. 18A shows the drive member 1806′disposed within the lumen of the shaft 1702′, however it is understoodthat the drive member can be removably and replaceably disposed withinthe lumen of shaft 1702′. In this embodiment, the elongate drive member,as a separate member, may be passed through the lumen of the shaft 1702′so as to extend distally beyond the external threads 1804′ at the distalend of shaft 1702′. As a separate element, the drive member can bemanipulated independently of the shaft 1702. For example, when the drivemember 1806′ is engaged with the recess of the threaded shank, the drivemember 1806′ can be manipulated such as by rotating handle 1811 toadvance the threaded shank of the bone anchor.

By driving each of the alignment shafts 1702A, 1702B into the polyaxialscrews 1602A, 1602B such that the engagement portion of each alignmentshaft interfaces with both the threaded shanks 1604A, 1604B and thereceiving members 1606A, 1606B of the screw, the alignment shafts canensure that the longitudinal axes of the threaded shanks 1604A, 1604B,receiving members 1606A, 1606B, and extension tubes 1608A, 1608B areeach coaxial with the longitudinal axes 1706A, 1706B of the alignmentshafts. This is the configuration shown in FIG. 17.

An alignment shaft similar to shafts 1702A, 1702B can provide an easyway to ensure the coaxial alignment of a screw extension tube, receivingmember, and threaded shank, but the alignment shaft cannot be used aftera spinal fixation element is passed through the receiving member becausethe spinal fixation element blocks access to the recess or other drivingfeature formed in the head of the threaded shank. Accordingly, themethod can include capturing the position and/or angular orientation ofone or more polyaxial screws and extension tubes when alignment shaftsare present using an instrument that can be re-applied after spinalfixation shaft capture, or some other procedure, prevents the use of thealignment shafts.

For example, and as shown in FIG. 19, the method can include coupling apolyaxial screw alignment instrument 1900 to the proximal ends of eachof the polyaxial screw extension tubes 1608A, 1608B and selectivelylocking the instrument 1900 to indicate a distance between and anangular orientation of each of the extension tubes relative to alongitudinal axis 1902 of the instrument 1900. This can be accomplished,for example, using a connection cap of the instrument 1900, such as theconnection caps 1904A, 1904B, to couple the instrument to the proximalends of one or more extension tubes, such as extension tubes 1608A,1608B. The measurements captured in this manner lie only in a singleplane, however. For example, in the embodiment shown in FIG. 19, themeasurements are captured in the transverse plane of the body, whichextends along the longitudinal axis 1902 of the elongate frame 1906.

In addition to the mechanical devices described above that indicate adistance between and an angular orientation of each of the extensiontubes relative to a longitudinal axis 1902 of the instrument 1900, aperson of skill in the art will appreciate that a variety of electricaland/or optical devices can be utilized as well. For example, sensors(not shown) can be placed on the alignment shafts and/or the caps 1904A,1904B (or other clamping devices) that secure the extension tube to thealignment frame, such that when the alignment shafts are placed and theheads and shanks are coaxial, the sensors can record the angularposition of the anchors. That is, the sensors can measure, for example,the angle of the coupling relative to the alignment instrument, theposition of the coupling along the length of the alignment instrumentframe (e.g., to indicate the distance between adjacent alignment shaftsor other components equipped with such a sensor), etc. A variety ofsensors that can be used for such applications are known in the art andcan include sensors, such as gyroscopes and tilt sensors used in smartphone technology.

Accordingly, the method can also include indicating and/or capturing anangular orientation of the polyaxial screw alignment instrument 1900 ina plane transverse to the longitudinal axis of the instrument, i.e.,transverse to the longitudinal axis 1902. The instrument 1900 caninclude a transverse angle indicator, such as the bubble level 1908, toprovide such an indication. The bubble level 1908 can be rotatablymounted to the elongate frame 1906 such that it rotates in a planetransverse to the longitudinal axis 1902. In the illustrated embodiment,the hemispherical bubble level 1908 can rotate in a plane perpendicularto the longitudinal axis 1902, thereby indicating the angularorientation of the instrument 1900 in the sagittal plane of the body. Touse the bubble level 1908, a user can rotate the bubble level 1908 untilthe air bubble trapped therein indicates that the bubble level is in alevel orientation. The bubble level 1908 can then be locked in thisorientation, or a corresponding angular orientation can be read from ascale coupled to the bubble level 1908. One of skill in the art willappreciate that instead of a bubble level, electronic sensors, such asgyroscopes and tilt sensors used in smart phone technology can be usedto capture and/or indicate angular orientation.

After capturing the position and/or angular orientation of the polyaxialscrews 1602A, 1602B and attached extension tubes 1608A, 1608B, thepolyaxial screw alignment instrument 1900 can be removed from theproximal ends of the tubes 1608A, 1608B. The instrument 1900 can beremoved with the connection caps 1904A, 1904B and bubble level 1908locked in their captured orientations, or the orientations can berecorded (e.g., using various distance and angular markings made on thevarious components of the instrument 1900) and the device removed withthe connection caps and/or transverse angle indicator in an unlockedstate. Moreover, in some embodiments, the extension tubes 1608A, 1608Bcan remain attached to the instrument 1900, and the instrument 1900 andextension tubes 1608A, 1608B can be decoupled from the receiving members1606A, 1606B of the polyaxial screws 1602A, 1602B. Further, thealignment shafts 1702A, 1702B can also be removed and the spinalfixation procedure can proceed as known in the art.

If a surgeon or other user desires to return the polyaxial screws 1602A,1602B to a coaxial orientation at a later point in the procedure (e.g.,after shaft capture and before applying corrective forces to the screwsto adjust the position and/or orientation of the vertebra), thepolyaxial screw alignment instrument 1900 can be used on its own toreturn the screws to the desired orientation. This can be advantageousbecause the alignment shafts 1702A, 1702B cannot be used due to theshaft or other spinal fixation element seated within the receivingmembers 1606A, 1606B of the screws.

To return the polyaxial screws to a coaxial orientation, the polyaxialscrew alignment instrument 1900 can be re-coupled to the proximal endsof the extension tubes 1608A, 1608B in the same manner as describedabove. In order to do so, a surgeon can adjust the position of eachextension tube 1608A, 1608B (and thus, each receiving member 1606A,1606B) to match up with the locked positions and orientations of theconnection caps 1904A, 1904B. Alternatively, if the connection caps1904A, 1904B were unlocked upon removal of the instrument 1900, the capscan be reattached to the extension tubes 1608A, 1608B and thenrepositioned until the distance and angle markings on the instrument1900 match those recorded when the alignment shafts 1702A, 1702B were inplace.

Adjusting the extension tubes 1608A, 1608B as described above willreturn the extension tubes to the correct orientation relative to thelongitudinal axis 1902 of the instrument 1900, i.e., relative to thetransverse plane of the body. In order to complete the positioning ofthe polyaxial screws 1602A, 1602B, the instrument 1900 (and thus theconnected extension tubes 1608A, 1608B) can be adjusted in a planetransverse to the longitudinal axis 1902, i.e., in the sagittal plane ofthe body, until the bubble level 1908 of the transverse angle indicatormatches the previously-captured orientation.

Once this is completed, a surgeon can be sure that the components ofeach of the polyaxial screws 1602A, 1602B are in coaxial alignmentdespite the absence of the alignment shafts 1702A, 1702B. In someembodiments, a surgeon can lock each of the polyaxial screws 1602A,1602B in this orientation by inserting a set screw (e.g., the outer setscrew 214 of FIG. 2) through the extension tubes 1608A, 1608B to lockthe orientation of the receiving member and threaded shank.

In another embodiment, a method for aligning polyaxial bone screws canutilize an image guidance system (IGS) or other precision positioningsystem that can identify the position and orientation of surgicaldevices within an operating space. FIG. 20 illustrates one embodiment ofa polyaxial screw extension tube 2000 that includes an array 2002 ofreflective members 2004A, 2004B, 2004C positioned in a predeterminedarrangement that can be recognized by an image guidance system. Thescrew extension tube 2000 can be similar to the screw extension tube 400described above, save for the presence of the array 2002.

An exemplary image guidance system can also include, for example, astereoscopic infrared (IR) camera capable of visualizing the reflectivemembers 2004A, 2004B, 2004C of the array 2000. By visualizing thereflective members, the system can utilize their predeterminedarrangement in the array 2002 to determine the exact position andorientation of the extension tube 2000 in the operating space.

As an alternative to such an image guidance system, one of skill in theart will appreciate that “smart” extension tubes, which are able todetermine and record a set position and orientation, can be utilized.For example, position and/or angular sensors may be placed on theextension tubes. Once a desired orientation is established for thealignment shaft, a surgeon or other medical professional can activate a“set” button, which will capture the orientation of the tube for a givenscrew and the system will record the position for future use and/orreference. A person of skill in the art will further appreciate that thesensors used in such an embodiment can be “active,” rather than simplypassive. That is, such sensors can actively record the position andorientation of the extension tubes and wirelessly communicate thisposition and orientation to an interface that provides guidanceinformation to a surgeon.

A method for aligning polyaxial screws using such a system can includecoupling an extension tube, such as the extension tube 2000, to areceiving member of a polyaxial screw, such as the receiving member 108of the polyaxial screw 100. The method can further include coupling analignment shaft to the polyaxial screw such that the alignment shaftmaintains a longitudinal axis of the receiving member and a longitudinalaxis of a threaded shank of the polyaxial screw in a coaxialorientation. For example, the alignment shaft 1702 can be insertedthrough the extension tube 2000 to interface with both the receivingmember 108 and threaded shank 102 of the polyaxial bone screw 100 suchthat the components are held in coaxial alignment.

Once the threaded shank 102, receiving member 108, and extension tube2000 are in alignment, the three-dimensional position and angularorientation of the extension tube 2000 can be measured using thesurgical image guidance system. That is, the reflective members 2004A,2004B, 2004C can be imaged and the position of the extension tube 2000can be calculated.

A surgeon can then remove the alignment shaft 1702 and proceed with thespinal procedure as known in the art. For example, the surgeon canproceed to pass a spinal fixation element through the receiving member108 of the polyaxial screw 100. If the surgeon desires to return thecomponents of the polyaxial screw 100 to coaxial alignment, the methodcan include measuring the three-dimensional position and angularorientation of the extension tube 2000 using the surgical image guidancesystem a second time. The surgical image guidance system can thencalculate the difference between the measurements of the position andorientation of the extension tube 2000 and provide direction to thesurgeon to aid in returning the polyaxial screw 100 to a coaxialorientation. The direction provided by the system can include, forexample, visual and auditory prompts that include changes in direction,distance, and angle necessary to return the polyaxial screw to a coaxialorientation. In response, the surgeon can adjust the extension tube 2000to place the longitudinal axis of the receiving member 108 and thelongitudinal axis of the threaded shank 102 in a coaxial orientationbased on guidance from the surgical image guidance system. This processcan be repeated as many times as necessary to move the extension tube2000 (and coupled polyaxial screw 100) into a coaxial orientation.

Following repositioning, the method can include, in some embodiments,inserting a set screw into the receiving member 108 of the polyaxialscrew 100 after adjusting the extension tube 2000 to achieve a coaxialorientation of the receiving member 108 and the threaded shank 102. Theset screw, such as the outer set screw 214 shown in FIG. 2, canindependently lock the orientation of the receiving member 108 relativeto the threaded shank 102 while still allowing the receiving member 108to move relative to a captured spinal fixation element in response tocorrective forces applied by a surgeon.

The methods and devices described herein can be utilized in a variety ofoperations—both in the spine and in other areas of the body. In theembodiments described above, reference is made to two polyaxial screwsbilaterally implanted in a single vertebral body. While this is oneexample of a configuration of one or more polyaxial bone screws,additional configurations are also possible. Furthermore, in theembodiments described above, reference is made to the polyaxial screwalignment instrument being applied such that a longitudinal axis of theinstrument lies within the transverse plane of the body and such thatthe transverse angle indicator measures an angular orientation in thesagittal plane of the body. This is also one of several possibleorientations for use of the devices and methods described herein.

FIG. 21, for example, illustrates an alternative embodiment of apolyaxial screw alignment instrument 2100 that is coupled to a pluralityof polyaxial screw extension tubes 2102A, 2102B, 2102C that areimplanted in a plurality of adjacent vertebrae on one side of the spinalcolumn 2104. In this embodiment, the longitudinal axis of the elongateframe 2106 lies in the sagittal plane of the body and thus capturesrelative distances and angles between the plurality of extension tubes2102A, 2102B, 2102C in this plane. Correspondingly, the transverse angleindicator 2108 indicates the angular orientation of the elongate frame2106 in the transverse plane of the body. Still further, the polyaxialscrew alignment instrument 2100 includes an alternative embodiment of aconnection cap 2110A, 2110B, 2110C that couples to each of the screwextension tubes 2102A, 2102B, 2102C along a mid-portion thereof, ratherthan at a proximal end thereof. One of skill in the art will appreciatethat embodiment described in FIG. 21 may not be effective when more thantwo polyaxial screw extension tubes are implanted on adjacent vertebralbodies. Further, one of skill in the art will appreciate that othermodifications are also possible and these too are considered within thescope of the invention.

All papers and publications cited herein are hereby incorporated byreference in their entirety. One skilled in the art will appreciatefurther features and advantages of the invention based on theabove-described embodiments. Accordingly, the invention is not to belimited by what has been particularly shown and described, except asindicated by the appended claims.

What is claimed is:
 1. A polyaxial screw alignment instrument,comprising: an elongate frame having a longitudinal axis extendingtherethrough; a plurality of connection caps slidably disposed along theelongate frame, each connection cap being configured to removably coupleto a polyaxial screw extension tube and to selectively lock relative tothe elongate frame such that a distance between the plurality ofconnection caps and an angular orientation of each connection caprelative to the elongate frame is maintained; and a transverse angleindicator configured to indicate an angular orientation of the elongateframe in a plane transverse to the longitudinal axis of the elongateframe.
 2. The instrument of claim 1, wherein the plane is perpendicularto the longitudinal axis of the elongate frame.
 3. (canceled)
 4. Theinstrument of claim 1, wherein the transverse angle indicator comprisesan angular scale coupled to the elongate frame.
 5. The instrument ofclaim 1, wherein the transverse angle indicator comprises an arm coupledto the elongate frame and an operating surface.
 6. The instrument ofclaim 1, wherein each of the plurality of connection caps includes athumbscrew configured to selectively lock the connection cap relative tothe elongate frame when tightened.
 7. A polyaxial screw alignmentsystem, comprising: a plurality of polyaxial screws having a threadedshank and a receiving member coupled to the threaded shank that can movepolyaxially with respect to the threaded shank; a plurality of extensiontubes, each extension tube configured to be coupled to the receivingmember of one of the plurality of polyaxial screws such that alongitudinal axis of the extension tube and a longitudinal axis of thereceiving member are maintained in a coaxial orientation; a plurality ofalignment shafts, each alignment shaft configured to be coupled to oneof the plurality of polyaxial screws such that a longitudinal axis ofthe threaded shank and a longitudinal axis of the receiving member aremaintained in a coaxial orientation; and a polyaxial screw alignmentinstrument having an elongate frame and a plurality of connection capsslidably disposed thereon, each connection cap configured to be coupledto a proximal end of one of the plurality of extension tubes andselectively locked relative to the elongate frame to maintain a distancebetween the plurality of connection caps and an angular orientation ofeach of the connection caps relative to the elongate frame; and atransverse angle indicator that indicates an angular orientation of theelongate frame of the polyaxial screw alignment instrument in a planetransverse to a longitudinal axis of the elongate frame.
 8. (canceled)9. The system of claim 7, wherein the transverse angle indicatorcomprises an angular scale coupled to the elongate frame.
 10. The systemof claim 9, wherein the transverse angle indicator comprises a verticalplumb.
 11. The system of claim 7, wherein the transverse angle indicatorcomprises an arm coupled to the elongate frame and an operating surface.12. The system of claim 7, wherein each of the plurality of alignmentshafts threadably engages with the receiving member of one of theplurality of polyaxial screws.
 13. The system of claim 12, wherein eachof the plurality of alignment shafts includes a protrusion formed on adistal end thereof that interfaces with a recess formed in the threadedshank of the polyaxial screw. 14.-17. (canceled)
 18. A method ofaligning polyaxial screws, comprising: coupling an extension tube to areceiving member of a polyaxial screw, the extension tube comprisingfeatures recognizable to a surgical image guidance system; coupling analignment shaft to the polyaxial screw such that the alignment shaftmaintains a longitudinal axis of the receiving member and a longitudinalaxis of a threaded shank of the polyaxial screw in a coaxialorientation; measuring the three-dimensional position and angularorientation of the extension tube using the surgical image guidancesystem.
 19. The method of claim 18, further comprising: removing thealignment shaft from the polyaxial screw after measuring thethree-dimensional position and angular orientation of the extensiontube; passing a spinal fixation element through the receiving member ofthe polyaxial screw; measuring the three-dimensional position andangular orientation of the extension tube using the surgical imageguidance system a second time; and adjusting the extension tube to placethe longitudinal axis of the receiving member and the longitudinal axisof the threaded shank in a coaxial orientation based on guidance fromthe surgical image guidance system.
 20. The method of claim 19, furthercomprising inserting a set screw into the polyaxial screw afteradjusting the extension tube to maintain the coaxial orientation of thereceiving member and the threaded shank.
 21. The method of claim 18,wherein the polyaxial screw is implanted in a patient's vertebra.